The invention concerns a linear drive consisting of a primary part which can be arranged on a slider, where the slider can be moved on a guide system, and a fixed secondary part which co-operates with the primary part so that the slider can be moved on the guide system.
Such linear drives are commonly used in engineering. They are used for example in machining centres or machine tools in order to move and position the working spindle with high speed and high precision. The secondary part consists of an arrangement of magnets with changing polarity and is usually fixed. The secondary part co-operates with the primary part. The primary part consists of an electromagnetic drive in which the current flow is used to generate a magnetic field which co-operates with the magnetic field of the secondary part so that the slider moves on the guide system.
The invention is described below such that the primary part, i.e. the arrangement of coils and similar through which current flows, is located on the moving slider and the secondary part, i.e. the arrangement of magnets, is fixed. The invention is not however limited to this structure. It is also possible for the secondary part, i.e. the arrangement of magnets, to be arranged on the moving slider and the primary part to be fixed.
For example one or more parallel guide rails are used as a guide system. Between the primary and secondary parts is an air gap. This air gap is of relatively small dimension and finally determines the efficiency of the drive, too large an air gap leading to poorer efficiency and a higher power consumption.
With an arrangement where the movement path of the linear drive lies in a horizontal plane, the primary part for example is below the slider. The working spindle, for example of a cutting machine tool, is attached to the slider. The primary part is here attached to the underside of the slider by fixing means, for example bolts. The secondary is then usually located below the primary part.
The slider with attachments has a substantial weight of up to several tonnes. Currently, if the primary part must be maintained or replaced due to wear, this poses problems for the engineer. The primary part is installed below the slider such that this is not easily accessible. As well as the substantial weight of the slider with its attachments, it must also be noted that because of the secondary part, magnetic attraction forces act on all magnetisable elements and must also be overcome when removing the slider from the guide system.
This is particularly disadvantageous if the primary part is removed and falls onto the secondary part or is attracted by this. In this case the two parts adhere to each other so strongly that under some circumstances they can no longer be moved relative to each other, let alone be separated, without damaging the housing or the equipment itself. It is however necessary for these elements to remain moveable relative to each other in order to allow any dismantling or installation without removing the slider completely from the guide system.
The invention is based on the task of improving a linear drive of the type described above in such a way that the primary part can easily be installed or removed.
To solve this task it is proposed that the primary part can be separated from the slider and moved on a bearing relative to the slider.
The bearing only becomes active when the primary part must be moved relative to the slider. The arrangement of the bearing is selected so as to ensure that the primary part does not adhere to the secondary part.
In a preferred embodiment of the invention, it is proposed to provide a roller or plain bearing or a roller or plain bed as a bearing. Various different concepts are conceivable for the bearing design. It is for example possible to set the primary part on a roller track which acts as a bearing. Alternatively it is also possible to arrange on the primary part itself rollers which roll on a corresponding support surface. Here the term xe2x80x9crollerxe2x80x9d is not restricted to a cylindrical body but naturally comprises also wheels or ball rollers. Alternatively it is however also possible to provide a plain bearing for example using magnetic fields to support the primary part. It is also proposed that a moveable bed or similar is provided which can be inserted in the gap between the primary and secondary parts in order to support the primary part and move it relative to the slider. Also the bed here is equipped with smooth running bearing elements such as roller bearings, ball bearings, rolling contact bearings, needle bearings and similar in order to achieve maximum ease of movement of the bed with the primary part. The bed for example here rests on the secondary part or is held by guide elements arranged at the side of this.
It is favourable here that on movement of the primary part on the bearing a movement gap remains between the primary part and the secondary part the movement gap can be set by corresponding matching of dimensions between the air gap which exists when the linear drive is in operation and the co-operating bearing elements. This gap can be selected relatively low but contact between the primary part and the secondary part should be avoided due to the very high adhesion forces.
In a preferred design of the invention it is proposed to provide a distance or height adjustment of the rollers on the primary part to set a distance between the primary part and the support surface. As a result of such designxe2x80x94in the same way as lowerable running gearxe2x80x94the rollers provided on the primary part can be lowered onto the support surface or approach this when required (for example for vertical or suspended use) and thus allow safe removal of the primary part from the slider.
A further development of the invention provides that the bearing can be moved on the support surface or roller track essentially at right angles to the direction of the movement of the slider and can be brought into the area of the primary part when the primary part must be moved relative to the slider. As a result of such a design, the roller track or contact surface on which are arranged the rollers provided on the primary part does not in any way disrupt the linear drive in normal operation. As a result the precision in production of these elements need not be selected too high in order to guarantee secure operation of the linear drive which can have a considerable length.
The bearing support surface or roller track can be moved either in a slot-like guide and thus be designed essentially stationary on the secondary part or alternatively can be introduced as a separate component for the case of dismantling or installing the primary part under the slider. A movement at right angles to the direction of movement of the slider on the guide system ensures corresponding positioning. A fixed design is advantageous if it must be ensured that the bearing is available at any time in order for example to monitor or maintain the primary part at short notice. The dismantlability of the bearing roller path or support surface is advantageous if the space in the linear drive between the primary and secondary part is relatively narrow or only small tolerances or working gaps are available and an extra element arranged in this area is disruptive.
The invention is not restricted to the use of a linear drive, the slider of which executes a horizontal movement. In the same way the invention can be implemented in a vertical or oblique movement of the slider. The common feature of these applications is a simple support and movement of the primary part relative to the slider, which is achieved by the proposal according to the invention.
As well as the development of the linear drive according to the invention, the invention also proposes the use of a bearing, in particular a roller board, for the relative movement of a primary part to a slider of a linear drive, where the primary part can be released from the slider moveable on a guide system. In particular the use of the roller board in this area offers a favourable advantage as the roller board is firstly a bearing element which is not expensive to produce and also allows easy movement of the primary part relative to the slider.
The roller board is here for example designed like a plate with rollers or wheels arranged on the end and supported either on the secondary part or at the side on the guide surfaces next to the secondary part. The primary part rests on the plate. Alternatively it is proposed to equip the roller board with a multiplicity of rollers located in particular between the primary part and the support surface, for example the secondary part, during movement of the primary part. On movement of the primary part, in this design there is also a relative movement of the roller board to the primary part, whereby in such an example a correspondingly generously dimensioned roller board is advantageous in order to transport the primary part completely out of the area under the slider. For this it is proposed according to the invention to design the roller board at least twice as long as the primary part (viewed in the movement direction).
Further advantageous features of the invention are described in the sub-claims.